1. Field of the Invention
The invention relates generally to wind turbines, and more particularly to systems and methods for reducing wind pressure on wind turbine blades by selectively opening excessive wind portals in the turbine blades.
2. Related Art
Wind turbines of many types have been used to generate electricity. These turbines for generating electricity take many forms including the following:
Traditional-looking windmills operate with fan-like rotors that look like airplane propellers that face into or away from the wind. This type of turbine is one of the most common turbine configurations used today.
The Darrieus Turbine which looks roughly cylindrical, with wind-catching blades that span the length of the cylinder often described as looking like an egg beater. This vertical axis turbine has vertical blades that rotate into and out of the wind, the blades are placed roughly parallel in an arc to the axis. Guy cables are usually used to keep the turbine erect. In addition to keeping the turbine erect, the cables impose a large thrust loading on the main turbine bearings, causing increased wear on the bearings. With this type of turbine, replacing main bearings requires that the turbine be taken down. The Darrieus was invented in the 1920's and is not widely used today.
The Darrieus Turbine is also related to machines with straight vertical axis blades called Giromills or cycloturbines which use a wind vane to mechanically orient a blade pitch change mechanism. They were designed to be mounted on a tower or other device. The cylcoturbine was marketed commercially for several years, but never progressed beyond the research stage.
The Savonius Turbine is S-shaped if viewed from above. The turbine turns relatively slowly, but yields high torque. It has been proven useful for pumping water and other tasks, but its slow rotational speeds have not been proven to generate electricity cost effectively from wind power.
A concern inherent to any type of wind turbine is prevention of mechanical and/or structural failure. Another concern is safety. As wind turbines are intentionally placed in areas of high wind, they are subject to extreme environmental conditions ranging from sustained high wind events, to excessive short term gusts. Incidents of wind turbine failures, including fire, blade breakage and separation, and complete structural collapse are well known.
While the costs of construction and maintenance have always been obvious considerations as wind turbines continue to increase in size, as more turbines are placed within or closer to populated areas, issues of safety become a greater concern.